Lighting device and illumination apparatus using the same

ABSTRACT

A controller has a first mode and a second mode. First mode is of generating a PWM signal that has a duty ratio to be changed according to a luminous level for a light emitting element and has a constant amplitude. Second mode is of generating a PAM signal that has a constant duty ratio and has an amplitude to be changed according to the luminous level for the light emitting element. Controller is configured to apply one of PWM signal in first mode and PAM signal in second mode to a control terminal of a switching element, when the luminous level is a predetermined level or more. Controller is configured to apply the other of PWM signal in first mode and PAM signal in second mode to the control terminal of the switching element, when the luminous level is less than the predetermined level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2013-170667 filed on Aug. 20, 2013 and Japanese Patent Application No. 2013-170668 filed on Aug. 20, 2013, the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD

The disclosure relates generally to lighting devices and illumination apparatuses using the same and, more particularly, to a lighting device, which has a dimming function and an illumination apparatus using the same.

BACKGROUND ART

For example, JP2006-511078A (hereinafter, referred to as “document 1”) discloses a supply assembly, which is configured to supply electric power to an LED (light emitting diode) module. This supply assembly includes: a series circuit of a diode and a control switch; and a controller. The series circuit is connected across both ends of a DC power supply. The controller is configured to output a dual PWM (Pulse Width Modulation) signal to the control switch. In addition, a series circuit of an inductor and the LED module is connected across both ends of the diode.

The controller includes a pulse width modulator, to which a current reference signal from a current source, a detection current and a high frequency saw-tooth-wave signal are input. The pulse width modulator is configured to output a high frequency PWM signal to one input part of an AND gate. To the other input part of the AND gate, a low frequency PWM signal is input. The AND gate is configured to output the dual PWM signal that is obtained by combination of the high frequency PWM signal and the low frequency PWM signal. The dual PWM signal is input to a gate of the control switch via an amplifier.

In this supply assembly, it is possible to change the intensity of light to be output from the LED module by changing a low frequency component of the dual PWM signal to be output from the controller to the control switch.

Incidentally, generally, a luminance of an LED is higher than that of an incandescent lamp or a fluorescent lamp. Therefore, if the LED is lighted by the same luminous flux as the incandescent lamp or the fluorescent lamp, a user may sense that the LED is brighter than the incandescent lamp or the fluorescent lamp. For this reason, it is required to reduce the luminous flux by suppressing a drive current for the LED, in order to make the apparent brightness of the LED agree with the brightness of the incandescent lamp or the fluorescent lamp.

In a case of an illumination apparatus including one or more LEDs in which a rated current is 350 [mA] for example, it is required to set a lower limit of the current to be equal to or less than several microamperes to several milliamperes. However, it is hard to perform minute current control as described above, in a so-called burst light method of controlling light so that a load current intermittently flows through the LED module, as the supply assembly in the above-mentioned document 1.

In addition, when fade-in control or fade-out control is performed to the LED, it is required to control the drive current for the LED over a wide range of a minute current value to a rated current value in order to smoothly change the brightness of the LED.

When the rated current for the LED is 350 [mA] for example, it is required to adjust the drive current in a range of 100 [μA] to 350 [mA], and accordingly, the drive current should be controlled by the resolution of about 1/1000. For this reason, it is hard to smoothly change the brightness of the LED in the case of the supply assembly in the above-mentioned document 1.

SUMMARY OF THE INVENTION

It is an object of the present technology to provide a lighting device, which can light a light emitting element at a deeper (lower) luminous level and can smoothly change brightness of the light emitting element over a wide range, and an illumination apparatus using the same.

A lighting device according to an aspect of the present invention includes a DC power supply, a switching element and a controller. The DC power supply is configured to provide a DC voltage across output ends thereof. The switching element is connected in series with at least one light emitting element across the output ends of the DC power supply. The switching element includes a control terminal to which a control signal is applied for adjusting a current flowing through the at least one light emitting element. The controller is configured to generate, when receiving a dimming instruction signal of setting a luminous level for the at least one light emitting element, the control signal, and apply the control signal to the control terminal of the switching element. The controller has a first mode and a second mode. The first mode is of generating a PWM signal that has a duty ratio to be changed according to the luminous level and has a constant amplitude. The second mode is of generating a PAM signal that has a constant duty ratio and has an amplitude to be changed according to the luminous level. The controller is configured to apply, as the control signal, one of the PWM signal in the first mode and the PAM signal in the second mode to the control terminal of the switching element, when the luminous level is a predetermined level or more. The controller is configured to apply, as the control signal, the other of the PWM signal in the first mode and the PAM signal in the second mode to the control terminal of the switching element, when the luminous level is less than the predetermined level.

An illumination apparatus according to an aspect of the present invention includes the above-mentioned lighting device and a light-emitting part including the at least one light emitting element. The light-emitting part is lighted by electric power supplied from the lighting device.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures depict one or more implementations in accordance with the present teaching, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements.

FIG. 1 is a circuit diagram illustrating one example of a lighting device according to First Embodiment;

FIG. 2 is a graph illustrating a relationship between a gate voltage and a load current in the lighting device according to the First Embodiment;

FIG. 3 is an explanatory drawing for operation of the lighting device according to the First Embodiment;

FIG. 4 is an explanatory drawing for another operation of the lighting device according to the First Embodiment;

FIGS. 5A to 5D are circuit diagrams partly illustrating a DC power supply used for the lighting device according to the First Embodiment;

FIG. 6 is a graph illustrating a relationship between a gate voltage and a load current in a lighting device according to Second Embodiment;

FIG. 7 is an explanatory drawing for operation of the lighting device according to the Second Embodiment;

FIG. 8 is an explanatory drawing for another operation of the lighting device according to the Second Embodiment;

FIG. 9 is an explanatory drawing for operation of a lighting device according to Third Embodiment;

FIG. 10 is an explanatory drawing for another operation of the lighting device according to the Third Embodiment;

FIG. 11 is an explanatory drawing for operation of a lighting device according to Fourth Embodiment;

FIG. 12 is an explanatory drawing for another operation of the lighting device according to the Fourth Embodiment; and

FIG. 13 is a cross section view of an illumination apparatus, in an installed state, using the lighting device according to any one of the First to Fourth Embodiments.

DETAILED DESCRIPTION

Hereinafter, embodiments for a lighting device and an illumination apparatus using the same will be described with reference to drawings.

First Embodiment

FIG. 1 is a circuit diagram illustrating one example of a lighting device 1 according to the present embodiment. This lighting device 1 includes a DC power supply 11, a current-adjusting part 12, and a dimming controller 13. The lighting device 1 is configured to light a light-emitting part 3 at a luminous level according to a dimming signal S1 (dimming instruction signal) that is output from a dimmer 2.

The light-emitting part 3 includes a plurality of LEDs 31 (light emitting elements) that are connected in series (four LEDs in FIG. 1). The light-emitting part 3 is connected across output ends of the DC power supply 11, via a transistor Q2 (switching element) and a resistor R1. The number of the LEDs 31 constituting the light-emitting part 3 may be one, two, three, five or more. The light-emitting part 3 may be constituted by the LEDs 31 connected in parallel.

The DC power supply 11 is connected to an AC power source 10, and is configured to convert, into a DC voltage, an AC voltage supplied from the AC power source 10. The DC power supply 11 includes a so-called diode bridge DB1 that is constituted by four diodes, and a smoothing capacitor C1 is connected across output ends of the diode bridge DB1. In the DC power supply 11, a series circuit, which is constituted by a transistor Q1 and a primary winding n1 of a transformer Tr1, is connected across the output ends of the diode bridge DB1. Further, in the DC power supply 11, a diode D1 is connected to one end of a secondary winding n2 of the transformer Tr1, and a smoothing capacitor C2 is connected across both ends of the secondary winding n2.

In the DC power supply 11 according to the present embodiment, an N-channel type MOSFET is used as the transistor Q1, and a drive circuit 111 is connected to a gate terminal of the transistor Q1. The on/off switching of the transistor Q1 is controlled by a PWM signal output from the drive circuit 111. In the DC power supply 11, a DC voltage generated across both ends of the smoothing capacitor C2 is an output voltage of the DC power supply 11.

The current-adjusting part 12 includes a first current-adjusting part 123, a second current-adjusting part 122, the transistor Q2 and the resistor R1. The first current-adjusting part 123 includes a so-called totem pole output circuit that is configured by connecting a transistor Q3 with a transistor Q4 in series, where the transistor Q3 is a P-channel type MOSFET and the transistor Q4 is an N-channel type MOSFET.

A source terminal of the transistor Q3 is connected to an output end of an operational amplifier 122 b of the second current-adjusting part 122, and a source terminal of the transistor Q4 is connected to a negative electrode of a DC voltage source 122 a of the second current-adjusting part 122. Gate terminals of the transistors Q3 and Q4 are connected to the dimming controller 13. The on/off switching of the transistors Q3 and Q4 is controlled by a PWM signal S3 output from the dimming controller 13. In addition, a connecting point of the transistors Q3 and Q4 is connected to a gate terminal (control terminal) of the transistor Q2.

The second current-adjusting part 122 includes the DC voltage source 122 a, which is capable of changing an output voltage thereof according to a control signal S2 output from the dimming controller 13. A positive electrode of the DC voltage source 122 a is connected to a non-inverted input terminal of the operational amplifier 122 b. The negative electrode of the DC voltage source 122 a is connected to a negative electrode of the DC power supply 11. A connecting point of the transistor Q2 and the resistor R1 is connected to an inverted input terminal of the operational amplifier 122 b.

Here, in the present embodiment, an N-channel type MOSFET is used as the transistor Q2, and an output end of the first current-adjusting part 123 (the connecting point of the transistors Q3 and Q4) is connected to the gate terminal of the transistor Q2. In the transistor Q2, its impedance is changed according to the magnitude of a voltage output from the first current-adjusting part 123, and accordingly it is possible to adjust the magnitude of a current that flows through the light-emitting part 3.

When receiving the dimming signal S1 from the dimmer 2, the dimming controller 13 generates the control signal S2 and the PWM signal S3 corresponding to the dimming signal S1, and then outputs the control signal S2 to the second current-adjusting part 122, and outputs the PWM signal S3 to the first current-adjusting part 123. The dimming signal S1 is a signal denoting the magnitude of a load current that is made to flow through the light-emitting part 3, namely, brightness of the light-emitting part 3. In the present embodiment, the current-adjusting part 12 and the dimming controller 13 serves as a controller, and the dimming controller 13 serves as a luminous-level-determining part.

Next, operation of the lighting device 1 will be described with reference to FIGS. 2 to 4.

FIG. 2 is a graph illustrating a relationship between a gate voltage v1 of the transistor Q2 in the current-adjusting part 12 and a load current i1 flowing through the light-emitting part 3. From this graph, it can be seen that the gate voltage v1 is constant in a range where a value of the load current i1 is equal to or more than “i12”, and the gate voltage v1 is reduced with a reduction of the load current i1 in a range where a value of the load current i1 is less than “i12”.

Each of A and B in FIG. 3 shows a gate signal S4 sent to the transistor Q4 while dimming control is performed by the first current-adjusting part 123. When a value of the load current i1 is “i11”, as shown in A of FIG. 3, a duty ratio (t1/T1) of the gate signal S4 is large. When a value of the load current i1 is “i12” (<i11), as shown in B of FIG. 3, a duty ratio (t1/T1) of the gate signal S4 is small. In this way, it is possible to change the brightness of the light-emitting part 3 by changing the duty ratio in the gate signal S4 according to the magnitude of the load current i1. In the drawing, a time period t1 and a time period t2 denote an ON-period and an OFF-period, respectively, and a time period T1 denotes the sum of the time periods t1 and t2.

FIG. 4 shows the gate signal S4 sent to the transistor Q4 while the dimming control is performed by the second current-adjusting part 122. In this case, the magnitude of the load current i1 flowing through the light-emitting part 3 is changed by changing the magnitude of the gate voltage v1 (an amplitude vm) of the transistor Q2 according to the control signal S2, and therefore, it is possible to change the brightness of the light-emitting part 3.

In the present embodiment, the gate signal S4 shown in each of A and B of FIG. 3 is equivalent to a PWM signal that has a duty ratio to be changed according to the luminous level and has a constant amplitude. On the other hand, the gate signal S4 shown in FIG. 4 is equivalent to a PAM (Pulse Amplitude Modulation) signal that has a constant duty ratio and has an amplitude to be changed according to the luminous level.

When the luminous level according to the dimming signal S1 output from the dimmer 2 agrees with a full-lighting level, the output voltage of the DC power supply 11 is set to a rated voltage for the light-emitting part 3, and accordingly, a value of the load current i1 flowing through the light-emitting part 3 becomes “i11”, and the light-emitting part 3 is fully lighted.

From this state, when a user operates the dimmer 2 to dim the light-emitting part 3, the luminous level according to the dimming signal S1 output from the dimmer 2 becomes low. When receiving the dimming signal S1 from the dimmer 2, the dimming controller 13 generates the PWM signal S3 for reducing the duty ratio of the transistor Q2, and outputs the PWM signal S3 to the first current-adjusting part 123. In a range where a value of the load current i1 is equal to or more than “i12” and less than “i11”, the control signal S2 that is output to the second current-adjusting part 122 is set to be equal to the control signal S2 upon the full-lighting.

When receiving the PWM signal S3 from the dimming controller 13, the first current-adjusting part 123 makes the transistors Q3 and Q4 turn on/off according to the PWM signal S3. Accordingly, the duty ratio of the transistor Q2 becomes less, and then the load current i1 flowing through the light-emitting part 3 also becomes less, and therefore, the brightness of the light-emitting part 3 becomes decreased. The above-mentioned operation is performed within the range where a value of the load current i1 is equal to or more than “i12” and less than “i11”.

Next, when the user operates the dimmer 2 to more dim the light-emitting part 3, the luminous level according to the dimming signal S1 output from the dimmer 2 becomes lower. When receiving the dimming signal S1 from the dimmer 2, the dimming controller 13 outputs the PWM signal S3 to the first current-adjusting part 123. However, in this case, the dimming controller 13 outputs the PWM signal S3 of making a value of the load current i1 agree with “i12”. The dimming controller 13 further generates the control signal S2 of reducing the gate voltage v1 of the transistor Q2, and outputs the control signal S2 to the second current-adjusting part 122.

When receiving the control signal S2 from the dimming controller 13, the second current-adjusting part 122 adjusts the DC voltage source 122 a so that an output voltage thereof agrees with a value of the gate voltage v1 according to this control signal S2. Accordingly, the load current i1 flowing through the light-emitting part 3 becomes less, and therefore, the brightness of the light-emitting part 3 becomes decreased.

In the present embodiment, the luminous level when a value of the load current i1 is “i12” is defined as a predetermined level. This predetermined level is a lower limit of the luminous level, and the lower limit is set by the first current-adjusting part 123. In the present embodiment, the operation performed in a range where a value of the load current i1 is equal to or more than “i12” is defined as a first mode, and the operation performed in a range where a value of the load current i1 is less than “i12” is defined as a second mode.

As above, when the luminous level is equal to or more than the predetermined level, the lighting device 1 performs the dimming control with the first current-adjusting part 123. When the luminous level is less than the predetermined level, the lighting device 1 performs the dimming control with the second current-adjusting part 122 in addition to the dimming control with the first current-adjusting part 123, namely, combination of two dimming controls. Therefore, it is possible to light the LEDs 31 at a deeper (lower) luminous level and smoothly change brightness of the LEDs 31 over a wide range.

In the present embodiment, the output voltage of the diode bridge DB1 is stepped down by a flyback converter using the transformer Tr1 to be applied to the light-emitting part 3. However, instead of the flyback converter, a boosting chopper circuit 112 may be used as shown in FIG. 5A.

Alternatively, instead of the flyback converter, a boosting/step-down chopper circuit 113 may be used as shown in FIG. 5B, a step-down chopper circuit 114 may be used as shown in FIG. 5C, or a forward converter circuit 115 may be used as shown in FIG. 5D, for example. In any case, the same effect can be obtained by providing the current-adjusting part 12 between the light-emitting part 3 and such a circuit.

In the present embodiment, the case where the LED is used as the light emitting element is described, but the light emitting element is not limited to the LED. For example, an organic EL element or a laser diode (LD) may be used as the light emitting element.

As described above, the lighting device 1 according to the present embodiment includes the DC power supply 11, the transistor Q2 (switching element), the controller (current-adjusting part 12 and dimming controller 13). The DC power supply 11 is configured to provide a DC voltage across the output ends thereof. The transistor Q2 is connected in series with the LEDs 31 (at least one light emitting element) across the output ends of the DC power supply 11. The transistor Q2 includes the gate terminal (control terminal) to which a control signal is applied for adjusting a current flowing through the LEDs 31. The controller is configured to generate, when receiving the dimming signal S1 (dimming instruction signal) of setting the luminous level for the LEDs 31, the control signal and apply it to the gate terminal of the transistor Q2. The controller has the first mode and the second mode. The first mode is of generating a PWM signal that has a duty ratio to be changed according to the luminous level and has a constant amplitude. The second mode is of generating a PAM signal that has a constant duty ratio and has an amplitude to be changed according to the luminous level. The controller is configured to apply, as the control signal, one of the PWM signal in the first mode and the PAM signal in the second mode to the gate terminal of the transistor Q2, when the luminous level is the predetermined level or more. The controller is configured to apply, as the control signal, the other of the PWM signal in the first mode and the PAM signal in the second mode to the gate terminal of the transistor Q2, when the luminous level is less than the predetermined level.

Preferably, as the above-mentioned lighting device 1 according to the present embodiment, the controller includes the dimming controller 13 (luminous-level-determining part) and the current-adjusting part 12. The dimming controller 13 is configured to determine whether or not the luminous level is equal to or more than the predetermined level. The current-adjusting part 12 is configured to apply the PWM signal in the first mode to the gate terminal of the transistor Q2, for adjusting the current flowing through the LEDs 31, when the luminous level is determined to be equal to or more than the predetermined level by the dimming controller 13. The current-adjusting part 12 is configured to apply the PAM signal in the second mode to the gate terminal of the transistor Q2, for adjusting the current flowing through the LEDs 31, when the luminous level is determined to be less than the predetermined level by the dimming controller 13.

Preferably, as the above-mentioned lighting device 1 according to the present embodiment, the predetermined level is a lower limit of the luminous level, and the lower limit is set by the current-adjusting part 12 in the first mode.

Second Embodiment

A lighting device 1 according to the present embodiment will be described with reference to FIGS. 6 to 8. Because circuit configuration of the lighting device 1 is similar to that of the First Embodiment, explanation thereof will be basically omitted here and described with reference to FIG. 1 if necessary.

As shown in FIG. 1, the lighting device 1 according to the present embodiment includes a DC power supply 11, a current-adjusting part 12 and a dimming controller 13. The lighting device 1 is configured to light a light-emitting part 3 at a luminous level according to a dimming signal S1 that is output from a dimmer 2.

Next, operation of the lighting device 1 will be described with reference to FIGS. 6 to 8.

FIG. 6 is a graph illustrating a relationship between a gate voltage v1 of a transistor Q2 in the current-adjusting part 12 and a load current i1 flowing through the light-emitting part 3. From this graph, it can be seen that the gate voltage v1 is reduced with a reduction of the load current i1 in a range where a value of the load current i1 is equal to or more than “i12”, and the gate voltage v1 is constant in a range where a value of the load current i1 is less than “i12”.

Each of A and B in FIG. 7 shows a gate signal S4 sent to the transistor Q2 while dimming control is performed by the second current-adjusting part 122. When a value of the load current i1 is “i11”, as shown in A of FIG. 7, a value of an amplitude vm of the gate signal S4 is large. When a value of the load current i1 is “i12” (<i11), as shown in B of FIG. 7, a value of the amplitude vm of the gate signal S4 is small. In this way, it is possible to change the brightness of the light-emitting part 3 by changing the amplitude vm of the gate signal S4 according to the magnitude of the load current i1.

FIG. 8 shows a gate signal S4 sent to the transistor Q2 while dimming control is performed by the first current-adjusting part 123. In this case, the magnitude of the load current i1 flowing through the light-emitting part 3 is changed by changing the duty ratio (t1/T1) of the transistor Q2 according to the PWM signal S3. Therefore, it is possible to change the brightness of the light-emitting part 3.

In the present embodiment, the gate signal S4 shown in each of A and B of FIG. 7 is a PAM signal that has a constant duty ratio and has an amplitude to be changed according to the luminous level, and the gate signal S4 shown in FIG. 8 is a PWM signal that has a duty ratio to be changed according to the luminous level and has a constant amplitude.

When the luminous level according to the dimming signal S1 output from the dimmer 2 agrees with a full-lighting level, the output voltage of the DC power supply 11 is set to a rated voltage for the light-emitting part 3, and accordingly, a value of the load current i1 flowing through the light-emitting part 3 becomes “i11”, and the light-emitting part 3 is fully lighted.

From this state, when a user operates the dimmer 2 to dim the light-emitting part 3, the luminous level according to the dimming signal S1 output from the dimmer 2 becomes low. When receiving the dimming signal S1 from the dimmer 2, the dimming controller 13 generates a control signal S2 for reducing the gate voltage v1 of the transistor Q2, and outputs the control signal S2 to the second current-adjusting part 122. In a range where a value of the load current i1 is equal to or more than “i12” and less than “i11”, the PWM signal S3 that is output to the first current-adjusting part 123 is set to be equal to the PWM signal S3 upon the full-lighting.

When receiving the control signal S2 from the dimming controller 13, the second current-adjusting part 122 adjusts the DC voltage source 122 a so that an output voltage thereof agrees with a value of the gate voltage v1 according to this control signal S2. Accordingly, the load current i1 flowing through the light-emitting part 3 becomes less, and therefore, the brightness of the light-emitting part 3 becomes decreased. The above-mentioned operation is performed within the range where a value of the load current i1 is equal to or more than “i12” and less than “i11”.

Next, when the user operates the dimmer 2 to more dim the light-emitting part 3, the luminous level according to the dimming signal S1 output from the dimmer 2 becomes lower. When receiving the dimming signal S1 from the dimmer 2, the dimming controller 13 outputs the control signal S2 to the second current-adjusting part 122. However, in this case, the dimming controller 13 outputs the control signal S2 of making a value of the load current i1 agree with “i12”. The dimming controller 13 further generates the PWM signal S3 of reducing the duty ratio of the transistor Q2, and outputs the PWM signal S3 to the first current-adjusting part 123.

When receiving the PWM signal S3 from the dimming controller 13, the first current-adjusting part 123 makes the transistors Q3 and Q4 turn on/off according to this PWM signal S3. Accordingly, the duty ratio of the transistor Q2 becomes less, and then the load current i1 flowing through the light-emitting part 3 also becomes less, and therefore, the brightness of the light-emitting part 3 becomes decreased.

In the present embodiment, the luminous level when a value of the load current i1 is “i12” is defined as a predetermined level. In the present embodiment, the operation performed in a range where a value of the load current i1 is equal to or more than “i12” is defined as a second mode, and the operation performed in a range where a value of the load current i1 is less than “i12” is defined as a first mode.

As above, when the luminous level is equal to or more than the predetermined level, the lighting device 1 performs the dimming control with the second current-adjusting part 122. When the luminous level is less than the predetermined level, the lighting device 1 performs the dimming control with the first current-adjusting part 123 in addition to the dimming control with the second current-adjusting part 122, namely, combination of two dimming controls. Therefore, it is possible to light the LEDs 31 at a deeper (lower) luminous level and smoothly change brightness of the LEDs 31 over a wide range.

Also in the present embodiment, instead of a flyback converter using a transformer Tr1, any one of circuits shown in FIGS. 5A to 5D may be used. In any case, the same effect can be obtained by providing the current-adjusting part 12 between the light-emitting part 3 and such a circuit. Further, also in the present embodiment, the light emitting element is not limited to the LED. For example, an organic EL element or a laser diode (LD) may be used as the light emitting element.

Preferably, as the above-mentioned lighting device 1 according to the present embodiment, the controller includes the dimming controller 13 (luminous-level-determining part) and the current-adjusting part 12. The dimming controller 13 is configured to determine whether or not the luminous level is equal to or more than the predetermined level. The current-adjusting part 12 is configured to apply the PAM signal in the second mode to the gate terminal of the transistor Q2, for adjusting the current flowing through the LEDs 31, when the luminous level is determined to be equal to or more than the predetermined level by the dimming controller 13. The current-adjusting part 12 is configured to apply the PWM signal in the first mode to the gate terminal of the transistor Q2, for adjusting the current flowing through the LEDs 31, when the luminous level is determined to be less than the predetermined level by the dimming controller 13.

Third Embodiment

A lighting device 1 according to the present embodiment will be described with reference to FIGS. 9 and 10. Because circuit configuration of the lighting device 1 is similar to that of the First Embodiment, explanation thereof will be basically omitted here and described with reference to FIG. 1 if necessary.

As shown in FIG. 1, the lighting device 1 according to the present embodiment includes a DC power supply 11, a current-adjusting part 12 and a dimming controller 13. The lighting device 1 is configured to light a light-emitting part 3 at a luminous level according to a dimming signal S1 that is output from a dimmer 2.

Each of A and B in FIG. 9 shows a gate signal S4 sent to a transistor Q2 while dimming control is performed by a first current-adjusting part 123. FIG. 10 shows a gate signal S4 sent to the transistor Q2 while dimming control is performed by a second current-adjusting part 122. By turning on/off the transistor Q2 through those gate signals S4, a load current i1 flowing through the light-emitting part 3 has a rectangular wave form.

When the load current i1 has the rectangular wave form, there is a possibility that noises occur at a rise time and a fall time of the load current i1, and the noises may lead to problems depending on the purpose. In view of that, in the present embodiment, a time period T2 is provided to suppress the noises (see FIGS. 9 and 10). The time period T2 is of performing frequency modulation at the rise time of the gate signal S4 (control signal).

A frequency of the gate signal S4 during the time period T2 is set to be higher than that of the normal gate signal S4 for turning on/off the transistor Q2. Therefore, it is possible to suppress a peak value of the noises occurring at the rise time of the gate signal S4.

In the present embodiment, when the luminous level is equal to or more than a predetermined level, the lighting device 1 performs the dimming control with the first current-adjusting part 123. When the luminous level is less than the predetermined level, the lighting device 1 performs the dimming control with the second current-adjusting part 122 in addition to the dimming control with the first current-adjusting part 123, namely, combination of two dimming controls. Therefore, it is possible to light the LEDs 31 at a deeper (lower) luminous level and smoothly change brightness of the LEDs 31 over a wide range.

Also in the present embodiment, instead of a flyback converter using a transformer Tr1, any one of circuits shown in FIGS. 5A to 5D may be used. In any case, the same effect can be obtained by providing the current-adjusting part 12 between the light-emitting part 3 and such a circuit. Further, also in the present embodiment, the light emitting element is not limited to the LED. For example, an organic EL element or a laser diode (LD) may be used as the light emitting element.

In the present embodiment, the time period T2 is provided at the rise time of the gate signal S4. However, the time period T2 may be provided to at least one of the rise time and the fall time of the gate signal S4. That is, a position at which the time period T2 is provided is not limited to the rise time as the present embodiment.

Preferably, as the above-mentioned lighting device 1 according to the present embodiment, the first current-adjusting part 123 is configured to set a time period of performing the frequency modulation to at least one of the rise time and the fall time of the control signal to be output to the transistor Q2.

Fourth Embodiment

A lighting device 1 according to the present embodiment will be described with reference to FIGS. 11 and 12. Because circuit configuration of the lighting device 1 is similar to that of the First Embodiment, explanation thereof will be basically omitted here and described with reference to FIG. 1 if necessary.

As shown in FIG. 1, the lighting device 1 according to the present embodiment includes a DC power supply 11, a current-adjusting part 12 and a dimming controller 13. The lighting device 1 is configured to light a light-emitting part 3 at a luminous level according to a dimming signal S1 that is output from a dimmer 2.

Each of A and B in FIG. 11 shows a gate signal S4 sent to a transistor Q2 while dimming control is performed by a second current-adjusting part 122. FIG. 12 shows a gate signal S4 sent to the transistor Q2 while dimming control is performed by a first current-adjusting part 123. By turning on/off the transistor Q2 through those gate signals S4, a load current i1 flowing through the light-emitting part 3 has a rectangular wave form.

When the load current i1 has the rectangular wave form, there is a possibility that noises occur at a rise time and a fall time of the load current i1, and the noises may lead to problems depending on the purpose. In view of that, in the present embodiment, a time period T2 is provided to suppress the noises (see FIGS. 11 and 12). The time period T2 is of performing frequency modulation at the rise time of the gate signal S4 (control signal).

A frequency of the gate signal S4 during the time period T2 is set to be higher than that of the normal gate signal S4 for turning on/off the transistor Q2. Therefore, it is possible to suppress a peak value of the noises occurring at the rise time of the gate signal S4.

In the present embodiment, when the luminous level is equal to or more than a predetermined level, the lighting device 1 performs the dimming control with the second current-adjusting part 122. When the luminous level is less than the predetermined level, the lighting device 1 performs the dimming control with the first current-adjusting part 123 in addition to the dimming control with the second current-adjusting part 122, namely, combination of two dimming controls. Therefore, it is possible to light the LEDs 31 at a deeper (lower) luminous level and smoothly change brightness of the LEDs 31 over a wide range.

Also in the present embodiment, instead of a flyback converter using a transformer Tr1, any one of circuits shown in FIGS. 5A to 5D may be used. In any case, the same effect can be obtained by providing the current-adjusting part 12 between the light-emitting part 3 and such a circuit. Further, also in the present embodiment, the light emitting element is not limited to the LED. For example, an organic EL element or a laser diode (LD) may be used as the light emitting element.

In the present embodiment, the time period T2 is provided at the rise time of the gate signal S4. However, the time period T2 may be provided to at least one of the rise time and the fall time of the gate signal S4. That is, a position at which the time period T2 is provided is not limited to the rise time as the present embodiment.

Preferably, as the above-mentioned lighting device 1 according to the present embodiment, the first current-adjusting part 123 is configured to set the time period T2 of performing the frequency modulation to at least one of the rise time and the fall time of the control signal to be output to the transistor Q2.

Fifth Embodiment

An illumination apparatus 7 according to the present embodiment will be described with reference to FIG. 13. FIG. 13 is a cross section view of the illumination apparatus 7, in an installed state, according to the present embodiment. This illumination apparatus 7 includes: the lighting device 1 according to any one of the above-mentioned First to Fourth Embodiments; a light-emitting part 3; and a main body 4 of the apparatus. The lighting device 1 is connected to a dimmer 2 via a cable, and is configured to light the light-emitting part 3 at a luminous level according to a dimming signal S1 that is output from the dimmer 2.

The main body 4 is an aluminum die-cast product for example, and is formed into a bottomed cylindrical shape, and one surface thereof (a lower surface in FIG. 13) is opened. The main body 4 is embedded in a ceiling through an embedded hole 100 a which is provided in a ceiling material 100. The main body 4 houses a substrate 32 on which a plurality of LEDs 31 are mounted (three LEDs in FIG. 13). At an opening end of the main body 4, a light diffusing plate 33 is attached for diffusing light emitted from the LEDs 31. In the present embodiment, the substrate 32, on which the LEDs 31 are mounted, and the light diffusing plate 33 constitute the light-emitting part 3.

As shown in FIG. 13, in the illumination apparatus 7 according to the present embodiment, the lighting device 1 and the main body 4 housing the light-emitting part 3 are installed at a certain interval. The light-emitting part 3 is electrically connected to the lighting device 1 through power lines 5 that are connected to each other via a connector 6. In this way, when the lighting device 1 is installed to be separated from the main body 4, the main body 4 is required to house only the light-emitting part 3. Therefore, it is possible to reduce the height dimension of the main body 4, and further improve flexibility regarding installation of the lighting device 1.

As above, it is possible to provide the illumination apparatus 7, which can light the light-emitting part 3 at a deeper (lower) luminous level, and smoothly change brightness of the light-emitting part 3 over a wide range, by using the lighting device 1 according to any one of the First to Fourth Embodiments.

In the present embodiment, the lighting device 1 is installed to be separated from the main body 4. However, the lighting device 1 may be installed integrally with the main body 4. In the present embodiment, the wired dimmer 2 is used. However, a wireless dimmer may be used, which can communicate with the lighting device 1 by infrared rays, electric waves or the like. That is, the dimmer 2 is not limited to the wired type as the present embodiment.

As described above, the illumination apparatus 7 according to the present embodiment includes the lighting device 1 and the light-emitting part 3 including at least one LED 31 (light emitting element). The light-emitting part 3 is lighted by electric power supplied from the lighting device 1.

While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings. 

The invention claimed is:
 1. A lighting device, comprising: a DC power supply configured to provide a DC voltage across output ends thereof; a switching element connected in series with at least one light emitting element across the output ends of the DC power supply, the switching element including a control terminal to which a control signal is applied for adjusting a current flowing through the at least one light emitting element; and a controller configured to generate, when receiving a dimming instruction signal of setting a luminous level for the at least one light emitting element, the control signal, and apply the control signal to the control terminal of the switching element, the controller having a first mode and a second mode, the first mode being of generating a pulse width modulation (PWM) signal that has a duty ratio to be changed according to the luminous level and has a constant amplitude, the second mode being of generating a pulse amplitude modulation (PAM) signal that has a constant duty ratio and has an amplitude to be changed according to the luminous level, the controller being configured to apply, as the control signal, one of the PWM signal in the first mode and the PAM signal in the second mode to the control terminal of the switching element, when the luminous level is a predetermined level or more, the controller being configured to apply, as the control signal, an other of the PWM signal in the first mode and the PAM signal in the second mode to the control terminal of the switching element, when the luminous level is less than the predetermined level.
 2. The lighting device according to claim 1, wherein the controller comprises: a luminous-level-determining part configured to determine whether or not the luminous level is equal to or more than the predetermined level; and a current-adjusting part configured to apply the PWM signal in the first mode to the control terminal of the switching element, for adjusting the current flowing through the at least one light emitting element, when the luminous level is determined to be equal to or more than the predetermined level by the luminous-level-determining part, the current-adjusting part being configured to apply the PAM signal in the second mode to the control terminal of the switching element, for adjusting the current flowing through the at least one light emitting element, when the luminous level is determined to be less than the predetermined level by the luminous-level-determining part.
 3. The lighting device according to claim 2, wherein the predetermined level is a lower limit of the luminous level, the lower limit being set by the current-adjusting part in the first mode.
 4. The lighting device according to claim 1, wherein the controller comprises: a luminous-level-determining part configured to determine whether or not the luminous level is equal to or more than the predetermined level; and a current-adjusting part configured to apply the PAM signal in the second mode to the control terminal of the switching element, for adjusting the current flowing through the at least one light emitting element, when the luminous level is determined to be equal to or more than the predetermined level by the luminous-level-determining part, the current-adjusting part being configured to apply the PWM signal in the first mode to the control terminal of the switching element, for adjusting the current flowing through the at least one light emitting element, when the luminous level is determined to be less than the predetermined level by the luminous-level-determining part.
 5. An illumination apparatus, comprising: the lighting device according to claim 1; and a light-emitting part including the at least one light emitting element, the light-emitting part being lighted by electric power supplied from the lighting device.
 6. An illumination apparatus, comprising: the lighting device according to claim 2; and a light-emitting part including the at least one light emitting element, the light-emitting part being lighted by electric power supplied from the lighting device.
 7. An illumination apparatus, comprising: the lighting device according to claim 3; and a light-emitting part including the at least one light emitting element, the light-emitting part being lighted by electric power supplied from the lighting device.
 8. An illumination apparatus, comprising: the lighting device according to claim 4; and a light-emitting part including the at least one light emitting element, the light-emitting part being lighted by electric power supplied from the lighting device. 